Cathode-ray tube with deflection amplification and post-deflection acceleration

ABSTRACT

In a cathode-ray tube that includes a slotted post-deflection acceleration electrode and, upstream thereof, an adjacent quadrupolar lens for deflection amplification, in order to correct image distortion, there are provided two slotted correcting electrodes disposed at either side of said quadrupolar lens. The correcting electrode situated between the secondary acceleration electrode and the quadrupolar lens is at the same potential as the secondary acceleration electrode, while the correcting electrode upstream of said quadrupolar lens has a slot with a configuration similar, but oriented perpendicularly to that of the slot provided in the post-deflection acceleration electrode.

. United States Patent [1 1 Albertin et al.

1 1 CATHODE-RAY TUBE WHTH DEFLECTION AMPLIFICATION AND POST-DEFLECTION ACCELERATION [75] lnventors: Andre Albertin; Bernard Chartier,

both of Paris, France [73] Assignee: Thomson-CS1, Paris, France [22] Filed: Nov. 1, 1971 [21] Appl. No.: 194,737

[ Feb. 12, 1974 3,142,779 7/1964 Wcndt 313/86 X 3,243,646 3/1966 Shimizu et al. 313/86 X 3,356,880 12/1967 Webster 313/86 3,496,406 2/1970 Dcschamps 315/17 3,544,836 12/1970 Reisner 315/31 R Primary ExaminerCarl D. Quarforth Assistant Examiner-P. A. Nelson Attorney, Agent, or FirmEdwin E. Greigg [57] ABSTRACT In a cathode-ray tube that includes a slotted postdeflection acceleration electrode and, upstream thereof, an adjacent quadrupolar lens for deflection amplification, in order to correct image distortion, there are provided two slotted correcting electrodes disposed at either side of said quadrupolar lens. The correcting electrode situated between the secondary acceleration electrode and the quadrupolar lens is at the same potential as the secondary acceleration electrode, while the correcting electrode upstream of said quadrupolar lens has a slot with a configuration similar, but oriented perpendicularly to that of the slot provided in the post-deflection acceleration electrode.

6 Claims, 6 Drawing Figures CATHODE-RAY TUBE WITH DEFLECTION AMPLIFICATION AND POST-DEFLECTION ACCELERATION The present invention relates to improvements in cathode-ray tubes employing electrostatic deflection and having systems for deflection amplification and post-deflection acceleration.

Tubes of this kind generally comprise the following units arranged in the trajectory of the electron beam, between the electron gun and the fluorescent screen:

Two electrostatic deflection systems designed to deflect the electron beam in two mutually perpendicular directions, namely vertically and horizontally;

Two quadrupolar lenses for amplifying the vertical and horizontal deflections, these lenses are located respectively downstream of the first and second of the two aforesaid deflection systems, and

A post-deflection acceleration system arranged downstream of the second quadrupolar lens, that is, between said lens and the fluorescent screen.

A post-deflection acceleration system of this kind is I disclosed in the U. S. Pat. to Deschamps, No. 3,496,406, granted Feb. 17, 1970. It provides, in addi' tion to the conductive coating that lines the internal wall of the tube envelope between the second quadrupolar lens and the screen, an electrode of spherical form at least partially surrounding said second lens and exhibiting at its crown a rectangular slot through which the electron beam passes. 4

It has been found, however, that the deflection amplification achieved under these conditions by the combined action of said quadrupolar lens and the secondary acceleration electrode with its rectangular slot, as described in the aforesaid patent, involves certain distortions which produce relatively significant cushioning deformations in the image displayed on the fluorescent screen. It is noted that the term cushioning designates, in the context of a cathode-ray tube, the defeet which results from the variation of the sensitivity parallel to the axes of vertical and/or horizontal scanning. As a result, an image which should have a rectangular form is distorted by a stretch of its angles and a contraction of its axes.

In the device in accordance with the invention these drawbacks are overcome. The slot cut in the postdeflection acceleration electrode has a more elaborate geometric form which effects a first correction of the aforesaid distortion. Further, according to the invention, there is generated a corrective electric field at the second quadrupolar lens making it possible to perfect the correction initiated by the shape of said slot.

Briefly stated, according to the invention, the cathode-ray tube of the aforeoutlined known structure comprises two planar disc-shaped electrodes associated with the post-deflection acceleration electrode and disposed in the path of the electron beam emitted by the electron gun of the tube. The first of said disc-shaped electrodes is situated upstream (in front) of the second lens, while the second is located therebehind, but in front of the slot in said post-deflection acceleration electrode. The first disc-shaped electrode contains a slot of substantially the same shape as the one in said post-deflection acceleration electrode. The median planes of the two last-named slots are disposed at right angles to one another. The second disc-shaped electrode contains an opening which is symmetrical in relation to the directions of the vertical and horizontal scanning.

The invention will be better understood from the ensuing specification takenin conjunction with the drawing which illustrates, by way of a non-limitative example, an embodiment of the assembly of the aforesaid elements.

In the drawing:

FIGS. 1 and 2 are schematic longitudinal sectional views of the improved cathode-ray tube in accordance with the invention, taken, respectively, along the central vertical plane and the central horizontal plane of the tube;

FIG. 3 is an end elevation, seen from the tube screen, of the cup-shaped spherical component constituting the post-deflection acceleration electrode,

FIG. 4 is an end elevation, seen from the tube screen, of the first correcting electrode; and

FIG. 5a and 5b are end elevations seen from the tube screen, of variants of the second correcting electrode.

Turning now to FIGS. 1 and 2, the improved cathode-ray tube in accordance with the invention comprises an evacuated enclosure 1, of glass for example, within which there is disposed an emissive cathode 2 heated by a filament 3, a modulating (Wehnelt) electrode 4, focusing and accelerating electrodes 5,6,7, vertical deflection plates 8, a first quadrupolar electronic lens 9, horizontal deflection plates 10, a second quadrupolar electronic lens 1 1, a spherical, cup-shaped electrode 12 with a slot 13 and a fluorescent screen 14. The internal wall of the enclosure is lined with a conductive coating 15, graphite for example, extending from the screen 14 up to the level of the electrode 12. The trajectories corresponding to the maximum deflections B and B, of the electron beam are indicated with broken, arrow-pointed lines.

As explained in US. Pat. No. 3,496,406, supra, the dimensions of the spherical electrode 12 and its position in the tube are so designed that its geometric center coincides substantially with the center of horizontal deflection, which is the virtual point of intersection of the electron trajectories in the plane perpendicular to the plates 10.

In FIG. 3, the slot 13, cut in the crown of the spherical electrode 12 constituting the post-deflection acceleration electrode, has a four-sided arcuate elongated outline. Each side is formed as a circular arc. Viewed from the interior of the slot, the opposite long sides are convex, while the opposite short sides are concave. The arcs intersect one another substantially at right angles. The slot 13 is so oriented that its major axis is disposed in alignment with the horizontal scanning plane, as shown in FIG. 2.

The post-deflection acceleration electrode 12, together with an electrostatic screen electrode 16 having the same potential as electrode 12, almost entirely surrounds the quadrupolar lens 1 l. The electrode 16 functions as a screen between the second pair of the deflector plates and the quadrupolar lens 11 which amplifies the deflection. An electrostatic screen of this kind, which is known by itself, defines with the electrode 12 an equipotential space around the quadrupolar lens 11 when. placed at the same potential as the acceleration electrode 12. The screen electrode 16 consists of a disc provided with a conventional elongated rectangular slot as illustrated in FIGS. 1 and 2. Generally, the electrodes 12 and 16 are grounded.

In the equipotential space hereinbefore defined, there are arranged at either side of the quadrupolar lens 11 two correcting electrodes 17 and 19.

The correcting electrode 17 is formed as a disc (FIG. 4) in which there is cut a slot 18 of curvilinear outline similar to that of the slot 13 in the post-deflection acceleration electrode 12. In the slot 18, however, the long and short sides are connected to one another by small circular arcs which are experimentally determined and which improve the effect of the slot 18 on the electron beam. The two slots 13 and 18 are disposed at right angles to one another.

The correcting electrode 17 is mounted independently of the electrodes 12 and 16 and can therefore be placed at a different potential. Thus, at the level of the quadrupolar lens 11 an electric correcting field can be generated. This kind of field locally modifies the deflection .of the electron beam. Under these circumstances, with a suitable potential applied to the correcting electrode 17, the distortions which normally appear on the screen and which are introduced by the vertical trace of the electron beam during scanning, are effectively eliminated.

The correcting electrode 19 is also formed as a disc (FIGS. a, 5b) located inside the post-deflection acceleration electrode 12 itself, beyond the quadrupolar lens 11 and in front of the curvilinear slot 13. The correcting electrode 19 is connected to the post-deflection acceleration electrode 12 and is thus at the same potential as the latter. The geometry of the opening 20 (FIGS. 1 and 2) provided in the electrode 19 is determined experimentally so that the effect of the electrode 19 on the'penetration of the post-deflection acceleration field, corrects the residual distortions which normally appear on the screen and which are introduced by the horizontal trace of the electron beam during scanning.

It has been found that the geometry of the opening 20 in the electrode 19, can vary from a circular form 200 (FIG. 5a) to a quasi-rectangular curvilinear form 20b having rounded corners (FIG. 512). It has been found that depending upon the potential applied to the correcting electrode 17, between the aforenoted two limit configurations a slot shape can be experimentally determined for the effective correction of the residual distortion introduced by the horizontal electron beam trace. Between these two limits, much more complex shapes are possible. Those shown in the drawing have been simplified either by the adoption of the shape of FIG. 5a, which is a circle 20a as mentioned, or by adopting the shape shown in FIG. 5b which is a curvilinear rectangle 2011 with three radii r r r Thus, for example, the opening 20 in the electrode 19 illustrated schematically in FIGS. 1 and 2 has a shape similar to the curvilinear form 20b of FIG. 5b. but this shape can be also the circular form 20a.

The advantages achieved by the devices forming the subject of the present invention have been enumerated in the course of the present description and in the related drawings. It is be understood that variant embodiments of the devices and the form given to them are possible without departing from the scope of the invention.

What is claimed is:

1. In a cathode-ray tube of the known type that in cludes (a) an evacuated envelope, (b) an electron gun at one end of the envelope for emitting an electron beam, (c) a fluorescent screen at the other end of the envelope to be excited by the electrons of said beam, (d) a horizontal deflection system in the path of said electron beam, (e) a quadrupolar lens disposed in said path after said horizontal deflection system for amplifying the horizontal deflection of said electron beam, (f) a vertical deflection system in said path, (g) a quadrupolar lens disposed in said path after said vertical deflection system for amplifying the vertical deflection of said electron beam, one of said quadrupolar lenses being closer to said screen than the other, (h) a conductive coating forming part of a post-deflection acceleration system and lining the internal wall of said envelope from said screen to the quadrupolar lens closer to said screen and (i) a spherical cup-shaped postdeflection acceleration electrode forming part of said post-deflection acceleration system and at least partially surrounding the quadrupolar lens closer to said screen, said spherical cup-shaped electrode being provided with a slot, the configuration of which has an elongated outline formed of two opposite, arcuate, inwardly concave short sides and two opposite arcuate, inwardly convex long sides, and through which said electron beam passes subsequent to passing through the last-named quadrupolar lens, the improvement comprising A. a first planar disc-shaped electrode disposed in said path immediately before the quadrupolar lens closer to said screen and being provided with a slot having substantially the same configuration as that of the slot provided in said post-deflection acceleration electrode, the median plane of said slot in said post-deflection acceleration electrode and the median plane of said slot in said first planar discshaped electrode being at right angles with respect to one another and B. a second planar disc-shaped electrode disposed in said path between the last-named quadrupolar lens and the slot of said post-deflection acceleration electrode, said second planar disc-shaped electrode having an opening for the passage of said electron beam, said opening being symmetrical with respect to the directions of the vertical and horizontal scanning.

2. An improvement as defined in claim I, wherein adjacent sides of said slot meet substantially in right angles.

3. An improvement as defined in claim I, wherein the slot provided in said first planar disc-shaped electrode has arcuately rounded corners.

4. An improvement as defined in claim 1, wherein the opening provided in said second planar disc-shaped electrode has a circular configuration.

5. An improvement as defined in claim 1, wherein the opening provided in said second planar disc-shaped electrode has a configuration of a distorted rectangle having arcuate, inwardly concave sides and corners.

6. An improvement as defined in claim 1, including means for applying the same potential to said postdeflection acceleration electrode and to said second planar disc-shaped electrode and means for applying a potential to said first planar disc-shaped electrode other than that applied to said second planar discshaped electrode.

=k =l t= 

1. In a cathode-ray tube of the known type that includes (a) an evacuated envelope, (b) an electron gun at one end of the envelope for emitting an electron beam, (c) a fluorescent screen at the other end of the envelope to be excited by the electrons of said beam, (d) a horizontal deflection system in the path of said electron beam, (e) a quadrupolar lens disposed in said path after said horizontal deflection system for amplifying the horizontal deflection of said electron beam, (f) a vertical deflection system in said path, (g) a quadrupolar lens disposed in said path after said vertical deflection system for amplifying the vertical deflection of said electron beam, one of said quadrupolar lenses being closer to said screen than the other, (h) a conductive coating forming part of a post-deflection acceleration system and lining the internal wall of said envelope from said screen to the quadrupolar lens closer to said screen and (i) a spherical cup-shaped post-deflection acceleration electrode forming part of said post-deflection acceleration system and at least partially surrounding the quadrupolar lens closer to said screen, said spherical cup-shaped electrode being provided with a slot, the configuration of which has an elongated outline formed of two opposite, arcuate, inwardly concave short sides and two opposite arcuate, inwardly convex long sides, and through which said electron beam passes subsequent to passing through the last-named quadrupolar lens, the improvement comprising A. a first planar disc-shaped electrode disposed in said path immediately before the quadrupolar lens closer to said screen and being provided with a slot having substantially the same configuration as that of the slot provided in said postdeflection acceleration electrode, the median plane of said slot in said post-deflection acceleration electrode and the median plane of said slot in said first planar disc-shaped electrode being at right angles with respect to one another and B. a second planar disc-shaped electrode disposed in said path between the last-named quadrupolar lens and the slot of said post-deflection acceleration electrode, said second planar disc-shaped electrode having an opening for the passage of said electron beam, said opening being symmetrical with respect to the directions of the vertical and horizontal scanning.
 2. An improvement as defined in claim 1, wherein adjacent sides of said slot meet substantially in right angles.
 3. An improvement as defined in claim 1, wherein the slot provided in said first planar disc-shaped electrode has arcuately rounded corners.
 4. An improvement as defined in claim 1, wherein the opening provided in said second planar disc-shaped electrode has a circular configuration.
 5. An improvement as defined in claim 1, wherein the opening provided in said second planar disc-shaped electrode has a configuration of a distorted rectangle having arcuate, inwardly concave sides and corners.
 6. An improvement as defined in claim 1, including means for applying the same potential to said post-deflection acceleration electrode and to said second planar disc-shaped electrode and means for applying a potential to said first planar disc-shaped electrode other than that applied to said second planar disc-shaped electrode. 